// 2025/8/20
// 神奇的字母(二)

#include <iostream>
#include <vector>
using namespace std;

int main() {
    vector<int> words(26, 0);
    char tmp;
    while(cin >> tmp)
    {
        if('a' <= tmp && tmp <= 'z')
            words[tmp - 'a']++;
    }
    int guess = 0;
    for(int i = 1; i < 26; i++)
    {
        if(words[i] > words[guess])
            guess = i;
    }
    char ans = guess + 'a';
    cout << ans << endl;
}
// 64 位输出请用 printf("%lld")